ok i have a 01 cummins with aft big dog fuel system with draw straw running edge/juice attiude. I leave it on number 1 setting for most part. Ever once in while i'll cut it up.

But i've noticed latly that my fuel mileage is sucking bad. If feels like ever time i turn around im putting fuel in my truck. I rember back when i had it all stock i was getting clost to 400 so miles the tank. Which was great! now im getting around 275 to tank for i have fill up again so i wont loose prime from fuel level being so low.

Some times i wish i wouldnt never put fuel system/ programmer on my truck... It cost me to much take it back stock seeing i didnt keep my old fuel lines i took them off and my fuel/sending unit in take i would have buy another one those along with lift pump that was going out hole reason i up graded my fuel system. I've ck my air filter it's pretty clean ck both fuel filters. But still. Somethings gota give this poor fuel milage is killing me. And its annoying.

Think the old girl might get the boot soon and i might be going back to i hate say it a gas burner.... Anybody know y i might be getting such poor fuel milage? Am i missing anyparts? i've ck for fuel leaks, i dont have any. Both fuel filters are clean.... I just dunno im throwing the "give: in.........

 

Have it checked for codes. VP44 may be bad.

 

How long have you had the mods, and did it start right after that? If you drive it even a little hard they will drink the hell out of some fuel. I have to be super easy on mine to get any kind of milage out of it.

 

Did you happen to put the bigger tires on about the same time, by any chance.

Mileage being cut in half, there is a definate problem here. Even a lead foot won't make that kind of difference. The most obvious mechanical things would be the VP44 or APPS issues. Any other problems then just bad mileage.

 

Did you have the speedo recalculated after installing the 315's? This will affect mileage also --- just a thought

 

This is what I'm suspecting to be part of the problem. His odometer isn't gonna show accurate miles driven if he hasn't had it recalibrated. If his truck is an automatic the larger tires also really jack with the shift points and that would create some mileage issues as well.

 

When you talk milage is really poor..... what type of numbers are you looking at? I've got a mostly stock 98.5 24v., and only get 20 if I'm going down-hill with a tail-wind. What about other guys here... what are y'all getting for numbers?

 

18-22mpg is about the average numbers for these truck years. Anything less then 17 and you better be lookin for a problem, unless your foot is the problem and that's a common thing.

 

My first problem was that I didn't realize my odometer/speedometer was off. After another speeding ticket today I've got to get that fixed. With the rough adjustment that I worked up, it looks like I'm usually around 17ish.

Going to get with a guy here locally to check on the fuel pressures.... and see if they know anything else. Dealer here didn't know squat.

I'm at about 98k miles and the truck runs pretty good, but, time to make sure it's really performing like it is supposed to.

On trips, if I'm on the highway running 70-75 on the speedo.... that translates to about 80-85 actual.... then I am looking in the 17 mpg range.... if I back it down to 55-60 actual, then I do get it up over 20 mpg, but damn if the scenery doesn't go by awefully slowly! I could walk that fast almost!

 

It always makes a pretty good difference when you back off the go pedal but to see that big a difference between the speeds you must be runnin the 3:50 or so gears in your truck. With my 4:10 gearing it doesn't make near that big of differance. Over 85mph I lose about 2mpg. I gave up those days though. Cops just don't have the sence of humor they used to have. They took all the fun out of it.